1. Field of the Invention
The present invention relates to a method and an apparatus for machining a non-circular workpiece, wherein a cutting tool is moved by a low speed actuator and a high speed actuator.
2. Discussion of the Prior Art
An apparatus of this kind is disclosed in the U.S patent application Ser. No. 07/471,392, which was filed on Jan. 29, 1990 U.S. Pat. No. 5,054,340 by the assignee of this application. In the apparatus, a cutting tool is moved in a moving direction perpendicular to the rotational axis of a workpiece by a piezoelectric actuator and a linear motor which are disposed in series in the moving direction of the tool. Namely, the linear motor is disposed on a base for moving a movable member which supports the cutting tool at its forward end, while the piezoelectric actuator is disposed at the forward end of the movable member to move the pool with respect to the movable member. Profile data defining a position change of the tool with respect to angular position change of the workpieces is decomposed by Fourier transformation into low frequency components and high frequency components so as to drive the piezoelectric actuator and linear motor, respectively. Since the piezoelectric actuator and linear motor are disposed in series in the moving direction of the tool, the tool is moved by a composite movement produced by the piezoelectric actuator and linear motor.
However, the apparatus has a problem that reaction force produced by the piezoelectric actuator deteriorates machining accuracy. Although the tool holder is designed to be light, the reaction force generated by the piezoelectric actuator becomes relatively large when the piezoelectric actuator is driven by a high-frequency drive signal. This reaction force is transmitted to the linear motor, as disturbance, thereby affecting the moving accuracy of the tool. Therefore, in the prior apparatus, it is difficult to improve the machining accuracy.